Here is some example how to do this:
Controller:
[HttpGet]
public string GetMandateListForCustomer(int userId, int customerId)
{
    var receiptBankUserList = new CustomerMandateReport()
    {
        GetMandateListForCustomer = _mandateManager.GetMandateListForCustomer(userId, customerId)
    };
    return RenderRazorViewToString("ViewName", receiptBankUserList);
}
// use this method to change your view into string
public string RenderRazorViewToString(string viewName, object model)
{
    ViewData.Model = model;
    using (var sw = new StringWriter())
    {
        var viewResult = ViewEngines.Engines.FindPartialView(ControllerContext, viewName);
        var viewContext = new ViewContext(ControllerContext, viewResult.View, ViewData, TempData, sw);
        viewResult.View.Render(viewContext, sw);
        viewResult.ViewEngine.ReleaseView(ControllerContext, viewResult.View);
        return sw.GetStringBuilder().ToString();
        }
    }
}
Method to render view as string is from here
Javascript
$('#btnAddElement').click(function () {
    $.get("UrlToAction?userIDd=123&customerId=321", function (data) {
        // replace element with class result with
        // our new html which we get from controller
        $(".result").html(data); 
    });
});